1. Field
The present invention relates to a system and method for sensing a change in a width of a strip of material from a desired width. More particularly, the present invention relates to a sensor that detects more light when the strip of material is narrower, and less light when the strip of material is wider.
2. Related Art
Composite tape strips are used to form composite parts, such as those used in the manufacture of aircrafts. In a lay-up process, strips of the composite tape are applied to a surface, layered, and then cured by pressure and heat to form a strong, light-weight composite part. Varying widths of composite tape strips may cause gaps or overlaps between adjacent tape strips. Gaps and/or overlaps can negatively affect the structural integrity of the composite part. Therefore, monitoring the width of composite tape strips may be useful during the manufacturing of a composite part to determine if the composite tape strip's width has varied from a desired value.
U.S. Pat. No. 4,033,697) (hereinafter the '697 patent) discloses one method for monitoring the width of strips of material. The '697 patent discloses monitoring the width of a hot strip of material, such as steel or glass, by using two sensing devices located above the strip and spaced apart a distance to provide viewing of each edge of the strip. The strip edges are imaged onto the detectors using visible and infrared radiation from the hot strips. Edge position information is determined for each edge. The edge position information is combined with a fixed dimension between the two sensing devices to calculate a total strip width. Unfortunately, the method disclosed in the '697 patent is relatively inexact. Additionally, the sensors disclosed in the '697 patent are cameras, which are quite large, limiting the locations within a strip-placement apparatus at which these sensors may be placed.
U.S. Pat. No. 5,120,976 (hereinafter the '976 patent) discloses a strip lay-up verification system with width determination. The system includes a sensor component having two edge detectors positioned on one side of a surface on which adjacent strips of material are laid. The system also includes a contrasting surface having different reflective properties than the strips of material. Each edge detector includes an illuminating device, comprising two arrays of LEDs, for illuminating an area including an edge of the strip of material. Each edge detector also includes an array of gradient refractive index lenses, which are fiber-optic devices having known focusing characteristics. The imaging device may be used for detecting the light reflected by an illuminated area and generating edge image signals from the detected light.
While the system disclosed in the '976 patent may be smaller than the system disclosed in the '697 patent, it is still limited in how small it may be manufactured, particularly because two edge detectors, each with two arrays of LEDs are required. Additionally, the angled configuration of the LED arrays, as illustrated in FIG. 1 of the '976 patent, may also limit how small such a device may be. Also, such a design may suffer from inaccurate readings due to errant reflections.
Accordingly, there is a need for an improved material width detector that overcomes the limitations of the prior art.